Furan and its derivatives are useful precursors for industrial chemicals in the area of, for example, pharmaceuticals, herbicides and polymers. Furan may be converted into tetrahydrofuran (THF) and 1,4-butanediol (1,4-BDO). THF and 1,4-BDO are valuable chemicals used industrially as solvents and in the production of elastic fibres such as elastane/spandex, polybutyrate terephthalate and derivatives of gamma butyrolactone (GBL).
These chemicals are usually produced industrially via a number of routes from petrochemical feedstocks, obtainable from fossil fuels. In recent years, increased efforts have focused on producing chemicals, including 1,4-BDO and THF, from renewable feedstocks, such as sugar-based materials.
A method for obtaining furan from non-fossil fuel based sources involves the decarbonylation of furfural. Examples of reaction processes for achieving this and the subsequent conversion of the furan into its derivatives can be found in Hoydonck, H E; Van Rhijn, W M; Van Rhijn, W; De Vos, D E; & Jacobs, P A; (2012) Furfural and Derivatives, in Ullmann's Encyclopedia of Industrial Chemistry (volume 16, pp 285-313), Wiley-VCH Verlag GmBH & Co. KGaA, Weinheim; Dunlop, A P; and Peters, F N; in The Furans Reinhold Publ. Co, 1953; K. J. Zeitsch, in “The Chemistry and Technology of Furfural and its Many By-products” Sugar Series 13, Elsevier, 2000; Lange, J-P; van der Heide, E; van Buijtenen, J; and Price, R; Furfural—A Promising Platform for Lignocellulosic Biofuels; ChemSusChem 2012, 5, 150-166 and Watson, J. M.; Ind. Eng. Chem. Prod. Res. Develop., 1973, 12(4), 310. Furfural may be obtained from hemicellulose via acid hydrolysis in the liquid phase as well as in the gas phase as described in WO2002022593 and WO2012041990.
The conversion of furan to THF and 1,4-BDO by hydrogenation in the presence of water, acetic acid and Raney nickel or oxide supported nickel catalyst is described in Watson, J M; Ind. Eng. Chem. Prod. Res. Develop., 1973, 12(4), 310.
A process for the conversion of furan into 1,4-BDO and THF is taught in U.S. Pat. No. 5,905,159. This document teaches a process in which furan is converted as a reaction mixture with water and in the presence of hydrogen but in the absence of a water-soluble acid in a single stage over a hydrogenation catalyst. The hydrogenation catalyst of U.S. Pat. No. 5,905,159 contains at least one element of subgroup I, V, VI, VII or VIII in the form of a compound or in elemental form, with the restriction that the catalyst does not contain nickel alone being applicable. The preferred catalyst in this process is Re/Ru on active carbon. A similar catalyst is used in the process described in Pan, T; Deng, J; Xu, Q; Zuo, Y; Guo, Q-X and Fu, Y; Catalytic Conversion of Furfural into a 2,5-Furandicarboxylic Acid-based Polyester with Total Carbon Utilisation; ChemSusChem 2013, 6, 47-50.
As well as THF and 1,4-BDO, other useful products such as n-butyl alcohol (NBA) and GBL may be produced in such hydrogenation processes.
More effective catalysts for the conversion of furan into 1,4-BDO and THF are taught in co-pending applications EP14196391.8, said catalysts incorporating rhenium and palladium on solid supports and EP14199023.4, said catalyst incorporating one or more metals from those in group 8, 9, 10 and 11 of the periodic table supported on amorphous or crystalline aluminosilicate supports.
In the reductive hydration of furan wherein 1,4-BDO is a desired product, furan and water need to be reacted in the presence of hydrogen and the catalyst. For such a process to proceed effectively, the water and furan are preferably in the same liquid phase. It is also preferred to use an excess of water to furan in this reaction in order to increase the selectivity to 1,4-BDO over THF. The majority of this water may be separated and recycled after removal of the reaction products. However, the solubility of furan in water and water in furan is too low and prevents a single liquid phase to be formed at concentrations suitable for a commercial process.
Further, separation of 1,4-BDO, THF and NBA in an efficient manner from an aqueous product stream provides an on-going challenge.
It is, therefore, an object of the present invention to provide a process for the production of 1,4-BDO from furan, which overcomes these problems associated with the solubility of furan in water (and vice versa) and the separation of the reaction products and provides an efficient and effective process.